How Domestication Shaped Your Family Dog

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Early in 2019, the Transportation Security Administration (TSA) announced its intention to use more floppy-eared dogs and fewer pointy-eared pooches to work as bomb sniffers in airports. They were making the change because pointy-eared dogs can appear "ominous," especially to children, and the TSA aims to project a calm and friendly environment to travelers as they go through security. No one wants to remind kids of the big bad wolf as they get ready to fly to grandma’s house.

How Did We End Up With Floppy-Eared Dogs?

Many of the dog shapes so familiar to us today have resulted from intentional breeding for specific features, including:

• Size.

• Coat texture.

• Ear structure; and

• Facial shape.

But dogs’ physical traits are also linked, in surprising ways, to drivers of their behavior.

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In the famous farm fox experiment begun in Siberia in the late 1950s, scientists took silver foxes raised for their fur and selectively bred the 10% that most strongly showed one trait: tameness. Within six generations, the selection and breeding process produced a population of animals that licked the hands of experimenters, tolerated being picked up and petted, whined when the humans left and wagged their tails when people returned. In other words, they were as tame as any domestic pup.

Domestication Syndrome

The experimenters also discovered that selection for tameness led to the emergence of physical traits that exemplify the domestication syndrome. In less than a decade, the tame foxes had floppy ears, curly tails and shortened snouts. Their levels of glucocorticoid (a stress hormone) had fallen to less than half that of wild foxes. Their adrenal glands had become smaller and their serotonin levels had increased, yielding less aggressive, “happier” animals. Like dogs, they also became capable of following the human gaze.

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How did these startling physical changes come about? In 2018, a study identified 429 genes that differ between modern dogs and modern wolves. These genes, linked to central nervous system maturation, affect the development of embryos and can confer tameness as well as smaller jaws, floppier ears and smaller skulls. The study concluded that, during early dog domestication, the selection was for behavior. The dual effects of these genes led to the physical traits observed in modern dogs.

Breeding Dogs that Look Like Perpetual Puppies

Another word for the collection of cute traits produced by the fox experiments is “paedomorphosis;” the retention of juvenile characteristics into adulthood. We can also take the reverse view, however, and start with appearance, examining the behaviors of dogs bred to look less (or more) like their wolf ancestors.

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In one experiment, scientists studied the physical traits and pack-signaling behaviors of dogs from 10 breeds, ranging from those that resemble wolves (German shepherds and Siberian Huskies) and those that look nothing like their lupine cousins (Cavalier King Charles Spaniels and Norfolk Terriers). They studied the threat and submission behaviors pack members use to establish and convey dominance and hierarchy.

The dogs that looked the least like wolves exhibited the fewest wolf-like patterns of behavior. Huskies, in contrast, displayed significantly more pack-like interactions; sled team owners often let their animals retain a pack social structure. It appears that the further the appearance of the domestic dog diverges from the wolf, the more elements of lupine body language disappear.

What About Homo Sapiens?

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Some scientists observe that we humans also appear to be subject to domestication syndrome. Paleoanthropologists believe that modern humans are less aggressive and more cooperative than many of our ancestors. And we, too, exhibit a significant physical change: though our brains are bigger than those of protohumans, our skulls are smaller and our brow ridges are less pronounced.

One hypothesis suggests that, as early people formed cooperative societies, evolutionary pressures favored mates whose features were less "alpha," or aggressive. These physical changes may have accompanied active selection in favor of prosocial and altruistic tendencies and against bullies and the genes associated with aggression.

Humans, it seems, didn’t just domesticate dogs and other animal friends; we also domesticated ourselves. As with our pets, our appearance shows it.